The invention relates to particle blast technology and, more particularly, to a method and apparatus for particle blasting utilizing crystalline ice particles.
Particle blast technology is well known and well used in industrial processes as a means for cleansing surfaces. Blast particle media include sand, grit, steel shots, nut shells, glass, plastic, corn starch, etc. These materials generally effect cleaning and surface preparation through an abrasive process wherein particles are projected by an air stream at a target surface resulting in surface erosion. However, abrasive processes are not practical or useful in certain applications as the degree of surface erosion effected is difficult to control and the occurrence of unintentional damage to the target surface may result. Also, a large amount of dust is is typically generated producing a hazardous and unfriendly working environment, both for the humans and for machinery.
In view of the above-mentioned deficiencies, alternative solid particle media have been proposed. In one variation of the technology, dry-ice (solid carbon dioxide) is pelletized into particles and used as the blast medium. On impact sublimation occurs and no dust is generated. Furthermore, such pellets are are relatively soft and, thus, do not tend to damage the surface to be cleaned under normal operating conditions. One drawback of this approach is that sublimation of dry ice results in the formation of a smoke-like vapor so that the object to be cleaned cannot be seen and consequently the cleaning procedure is adversely affected. Another consideration would be the relatively high cost representative of this particular blast medium.
A further variation provides the use of crystalline ice particles for effecting surface cleaning. Descriptions of various methods and apparatuses employing ice particles as the blast medium can be found in PCT patent application CA90/00174 entitled "Particle Blast Cleaning and Treating of Surfaces", publication number WO 90/14927 and publication date Dec. 13, 1990; PCT patent application CA90/00291 entitled "Apparatus for Preparing, Classifying and Metering Particle Media", publication number WO 91/04449 and publication date Apr. 4, 1991; and British patent application 2,171,624A published Sep. 3, 1986. Crystalline ice particles are considered an inexpensive and fairly non-abrasive blast medium which lends itself to dust-free surface cleaning and coating removal, and facilitates cleanup and waste management. However, the cleaning efficiency of an ice blasting method is low relative to the abrasive techniques previously mentioned. It is generally believed that production of ice particles with sharp edges and utilizing low temperatures to enhance the hardness and strength of the particles are factors that contribute to improved abrasiveness and therefore effectiveness of this blast medium. Enhancement of ice particle hardness is achieved in conventional devices by incorporating an air cooling unit in order to cool the blast air projecting the particles. Overheads associated with this air cooling unit provide additional cost, weight and size to the blasting apparatus, along with increasing the overall power consumption of the device.